Exemplary embodiments relate to a piezoelectric resonator element, a piezoelectric resonator, and a piezoelectric oscillator; where the piezoelectric resonator element is capable of forming a thickness shear vibration as a main vibration, declining the reaching of an attenuating vibration of the main vibration to a marginal edge of the piezoelectric resonator element, and reducing the vibration displacement in the attenuating vibration of the piezoelectric resonator element.
Related art piezoelectric resonators are widely used as a base-frequency-signal source in various electronic devices or communication devices. Among piezoelectric resonators, AT cut quartz crystal resonators can outstandingly maintain frequency stability in wide range of temperatures, and are outstandingly tolerant against time duration, and hence are widely used for various devices, such as electronic devices and mobile communication devices, etc.
AT cut quartz crystal resonator is commonly used with a thickness shear vibration mode as the main vibration. During the thickness shear vibration, a constant wave is generated right under the excitation electrode that is placed in the center of a resonator element, and the vibration is extracted as a resonance frequency. The vibration generated in the center of the resonator element is propagated to the marginal edge of the resonator element.
Here, it is necessary that the vibration, which is attenuated at the marginal edge of the resonator element, be sufficiently attenuated, so as to assure the electric characteristics necessary as a resonator. The resonator element is fixed and held to a housing container such as one made of ceramics, and the like, via a conductive adhesive, and the like, at the marginal edge of the resonator element. Consequently, if the vibration attenuation at the marginal edge of the resonator element is not sufficient, the vibration leaks out from the fixed portion of the marginal edge of the resonator element. For this reason, the vibration at the center of the resonator element is obstructed, and Crystal Impedance (referred to as “CI value” hereafter) is, generally, worsened. Moreover, another vibration mode is induced and the stability of oscillating-frequency is, generally, lowered.
In order to sufficiently attenuate the attenuating vibration of the thickness shear vibration at the marginal edge of the resonator element, the structure shown in Japanese Unexamined Patent Publication No. H9-93076 and the Japanese Unexamined Patent Publication No. 2001-257558 is disclosed. In this structure, by applying one groove along the outer rim of an excitation electrode, either the vibration at the marginal edge of the resonator element is suppressed, or the electric characteristic of the resonator is enhanced.